Does anybody run 3.73's in there 9 bolt rear end and if so how well does it perform? I was actually thinking of upgrading from my 3.27's since the rear is going to go through a rebuild anyway. I am a little afraid that it might be overkill but am not worried about top speed as much. Since these motors make gobbs of torque I wanted to get the best launch possible during racing. Anyone have feedback on this? Looking to do this very soon.

 

When driving on the highway @ 60 MPH in OD, your engine rpm will increase by 250 rpm if you swap in 3.73's for your 3.27 gears. You worry too much.

 

i thought 3.45 was the lowest gear made for the 9 bolt? hmmm

 

I thought that the 9 bolt had an aftermarket 3.73 option. Maybe I'm wrong. Somebody enlighten me on this. I want to get the best bang for my dollar without over reving out of my torque range.

 

A nine-bolt would be 3.70's, not 3.73's, although the difference would be miniscule.

JamesC

 

3.73's are over kill. Well with a 5 speed and 350 not sure how they would be with a automatic. stay with 3.42's at the most, plus 3.73's eat gas bad.

 

The L69, a 305 HO, was equipped with a 5-speed and 3.73's. Kicked 'Vette" butt back in the day. So overkill?

JamesC

 

I have them on my car. Actually 3.70 Borg Warner gears. I have the 700R4 and would not want to go any lower for a street vehicle. I can still get 20+ mpg on the highway with a motor that is putting out well past 400hp at the crank. If you had a six speed there is no issue and maybe you could go a little lower.

 

yep, 373's are pretty harsh with the low first gear of the 700r4.... I hear a lot of people say they love their 355's and 342's on the street especially with an auto, dunno bout a 5 speed, how does their first gear ratio compare?

 

James in what day did they kick the vettes butt LOL .... maybe in 84 but thats it ... if they did even then. the 5.0 ho cars were mid 15 second cars I never saw the appeal of the engine the was really nothing incredible or exhilerating about it, just a hopped up taxi engine LOL

 

Only 20mph on the highway with 400hp at the crank?

Just kidding I know you meant MPG.

I had a car with a TH350 and 4.10s, I would not want to drive that as a daily driver.

 

3.73s are fun. They're not overkill, but they are less economical than 3.42s, which still give good performance. I have 3.73s (stock) in my SS, and 3.42s in the 'bird. They both have their strong points. Obviously the lower gear helps in the bigger car.

 

yup 84 would be the year IIRC. The crossfire vette was pretty slow.

 

I went from 2:70 to 3:73s in my 9 bolt, got them from Differential Techniques. They are as quite as stock gears. I also have a 2600 hundred stall convertor. Definitely not overkill, fuel mileage drops noticably but 23 to 2400 rpms on the freeway is not bad.
Good gear with my 350. I have a very mild cam (214/220. 452/465) an Eldebrock base and AS&M runners, no headers good catback. I like them.
GWW

 

Thanks. I made the correction.

 

Strange made a 3.73 for the 9 bolt, costed me 350 for the gears. Its quite a holeshot with the 700 r4 with a 3.06 first gear. And the nice thing on the highway cruising at 60 i am only pulling 1700 rpm

 

I run 3.73's behind my 700R4. I love it! As long as you've got a good set of tires, a relatively stock 350, driven right, should still hook with that gear. I've got a 2500rpm stall with those gears, behind a mild 305, and it holeshots very well. The fuel mileage will expectedly drop some, but you've got to make a few daily-driver vs. toy compromises, and a rear-gear change can make a car feel like a new beast.

 

You're tach is wrong, or you're running some seriously tall tires. My SS has 3.73s and a 200-4R, with a more conservative overdrive than a 700-R4 I run about 2000 rpms at 60mph. My 'bird runs between 1800-1900 at 60mph with 3.42 gears and a 700-R4.

 

1700rpm sounds about right at 60mph ... my 84 when new turned like 2,000rpm at 65 in OD with 373's ... my 5 speed 373 turns about 2000-2100 at 65. But his tach might be a little off or he is running taller tires. Mine has 235/60/15's and din't the OD's change throughout the years? I've heard of 2 OD's used in the 5 speeds for V-8's ones like a .74 and the other is like a .63 or something like that.

 

I did a search for "Differential Techniques" , no luck.
Where are they located?
Web site?
All of the 3.70 gears I have got were all noisy as hell.
So I am looking for some that aren't.

 

Ditto the above comments........For your statement to be true, you'd have to be running 31" tall tires ! Are you?

 

+ 1. At 60mph I turn about 2200rpm, 70mph is right about 2500rpm

 

do a search in the tpi forum,, lots more info. and people who have made the switch. all i can say is